Luminescent material



March 8, 1938. H. w. Ll-:vERENz 2,110,161

LUMINESCENT MATERIAL Filed Jan. 51, 1955 HHENIUM CHRB ONH TE znco.3

Z112 04 Re Wr 'ron/EY Patented Mar. 8, 1938 l 29E URAUNITED STATESPATENT ori-ics LUMINESCENT MATERJLl Humboldt W. Leverenz, Collingswood,N. J., assignor to Radio Corporation of America, a corporation ofDelaware Application January 31, 1935, Serial No. 4,289

9 claims. (ci. 134-47) My invention relates to improvements in lumi-Second sten- Finely divided, puriiied silicon nescent materials. dioxide(silica) is added. The particles of silicon One of the objects oi myinvention is to provide dioxide are very small, preferably less than 100vmaterial adaptable particularly for the so-called microns in diameter.These particles may be ob 5 luminescent screens for cathode ray tubesused tained, for example, by grinding in a ball mill or 6 in televisionreceivers, and on which an image of the like, and then passing thematerial through the. transmitted object is reproduced, the maa `lOOmesh screen. In making the material "terial havingI advantages overthose proposed known as zinc orthoslicate, as hereinafter exheretoforein the Way of increased intensity, efplained, itis proposed to use thesilicon dioxide l ilciency, stability, and cathode-luminescence. inabout 0.5 to .6 grammolecular ratio to thev 10 Other objects andadvantages will hereinafter zinc. Likewise, in making compounds known asY appear. the metasilicates, as hereinafter explained. it is My improvedmaterial is an oxygen compound proposed to use the silicon dioxide inabout 1.0 comprising al metal and an element of the fourth to 1.2gram-molecular ratio to the metal. In the l vertical column in theperiodic system, and rhespecific case referred to, 2.26. grams ofsilicon dil5 lnium as an activator to give to the compound the oxide(S102) were added to the mixed solutions 'characteristics of becomingluminescent when exof zinc nitrate and rhenium nitrate. The combiposedto radiant energy. By radiant energy is nation was mixed well. meantsuch radiations as electron bombardment, As an alternative in this'step,it is proposed to 2g X-rays, or actinic light or similar radiations. addthe silicon dioxide in the form of colloidal The word activator as hereused, designates the silicon dioxide.

use of an element in relatively small quantities to As a furtheralternative, it is proposed to use increasel the luminous eiiieie'ncy ofthe luminesgermanium dioxide instead of silicon dioxide. cent material.It'appears that the addition of Third sten-The zinc and rhenium areprecipa small quantity of a suitable element commonly itated ascarbonatos, oxalates, sulphides, hydrox- 2. known as an activatorresults in the element ides or phosphates. When the metals are pre-.being held in a pseudo chemical bond, and apcipitated as carbonates,this is done by adding parently in a physical bond between theintersufficient ammonium carbonate or ammonium stices of the elementalcrystals comprising the carbamate (NHiHCOaNI-IiNHeCOz) for this P111'-luminescent material.- 'I'he amount of activator pose, 0r by'making theSolution Slightly alkaline "0 used may be varied over a very wide rangeand with ammonium hydroxide and then saturating .serves to control theproperties and characterthe same with carbon dioxide. In the specificistics of the resultant luminescent material. case referred to, ammoniumcarbamate was used My invention resides in the improved luminesin thisStep, 40400. 0f aDPIOXimaely 4-7 I10Ima1 5 cent material of thecharacter hereinafter deammohillmarbamate being added 120 the S0111- 35scribed and claimed. tion of the nitrates of zinc and rhenium, with theThe ngure of drawing is a pictorial illustration Silicon dioxide, Sexplained- The mixture Was of the action which it is understoodtekesplace then boiled and stirred, decahted While hot, and in thecourse of making my improved luminescent then evaporated to -drynesswhile stirring. in this material. step, the zinc and rhenium areprecipitated out 40 l In Carrying out my invention, the ingredients ofsolution as insoluble carbonatos, the remaining 'used are as pure as itis possible to obtain, the liquid containing only ammonium nitratestepsbeing as follows: In the precipitating action, it is understoodIP11-.111! step-Solutions of zinc nitrate, Zn(NO3).2, that the minutesilicon dioxide particles serve and rhenium nitrate, Re(NOa) 4, arewarmed toas nuclei about which the zinc and rhenium car- 45 gether andstirred to thoroughly mix the two. bonates agglomerato. That iS, it iSllrldBIStOOd Considering a specic case, 20.5 cc. of 3.68 molal that eachsilicon dioxide particle serves as a core -l zn(No3 2 and 4.32 oo. of0.1 molal of Re NO3 i to which there adheres one layer 0r Coating 0fwere mixed together. precipitated carbonates of zinc and rhenium. 5o: IAs alternatives in this step, it is proposed to This is represented atthe left in the figure of 50 l use, instead of the zinc, any othermetals such as drawing. The result is that, within the limita- 1`.magr:|esium, calcium, beryllium, strontium, or any tion of theprevious sub-division of the 4silicon other suitable metal in the rstthree groups of dioxide to practically molecular dimensions, a vtheperiodic system and to use, especially, the homogeneous mixture ofsilicon dioxide and the alkaline earth metals in group II of thissystem. carbonates of zinc and rhenium is obtained. 55

Fourth sten- The resulting material is elutriated or washed withdistilled water to remove practically all the ammonium nitrate. The lastwashing liquor is decanted, and the remaining mass is dried.

Fifth step-The dried material is then heated in a platinum or othersuitable crucible at a temperature from 900 to 2800 centigrade and for aperiod from 5 to 150 minutes, depending upon the amount of the materialand the characteristics of the heating furnace, as will be wellunderstood. In th'e specic case referred to,

the material was heated at about 1200 C. fon.

two hours, and then removed from the furnace and allowed to cool in theair. The resulting material gave a violent color of luminescence underbombardment by the electrons of a cathode ray beam.

In view of the fact that CO2 is driven off during this iinal heatingstep, it might very nat urally be inferred that the resulting compoundwould be a mixture of zinc and rhenium sil- Cates. Such is apparentlynot the case, since the final material seems to be a zinc orthosilicatewherein rhenium is entrained as an activator. The formula, ZnzSiOizRe,therefore, has been assigned to my improved synthetic Willemite, but itis to be definitely understood that I am not bound by any particulartheory of formation thereof. I have used the colon in the above formulato indicate the presence of the thus conjoined metal as rhenium as anactivator.

In cases where the zinc and rhenium are precipitated as sulphides, it isproposed, in this step, to heat the material in an atmosphere containingoxygen. This decomposes the sulphides and removes the sulphur as sulphurdioxide.

As an alternative in this step, and in the specie case referred to, `itis proposed to melt-a small quantity of the material, such as 0.1 to 5.0grams, at about l55o C. for about one hour, and then to remove thematerial from the furnace and cool it .rapidly by quenching, such'as byplunging the material immediately into Water at about 4 C. The resultingmaterial is characterized by the fact that it has an almost whitecathodo-luminescence. The color of luminescence, under bombardment bythe electrons of a cathode ray, might be said to be greenish yellow.

Where germanium dioxide is used instead of silicon dioxide, the finalresult is to obtain a luminescent material known as a zincorthogermanate, wherein rhenium is entrained as an activator. Theformula of this materialmay be expressed as ZnzGeO4zRe. As-analternative, where zinc is used it is proposed to replace the same bycadmium up to the extent of about 30%,. Also, in the first step, theefficiency of secondary emission may be increased by adding a smallamount of a suitable substance such as barium, strontium; caesium,cerium, thorium, rubidium, etc. Such a substance can also be added afterthe carbonatos have been formed, such as after the decantation of thelast washing water in the fourth step.

Where strontium is used instead of zinc, the resulting material is knownas strontium metasilica'te, SrSiOazRe.

Where magnesium is used instead of zinc, the resulting material is knownas magnesium orthosilicate, MgzSiOtzRe.

The formation of the material known as zinc orthosilicate, with rheniumas the activator, may be expressed as follows:

The formation of the material known as zinc orthogermanate, with rheniumas the activator, may be expressed as follows:

For the purpose of obtaining greater brilliancy l as the screen, made ofmy improved material, is scanned by a cathode ray, it is proposed, inthe making of the screen, to mix in with the various ingredients fromone percentto ten percent of an element or elements which yield' .X-raysunder cathode ray bombardment. Elements for this purpose may bemolybdenum, tungsten, thallium, tin, platinum, etc., or compounds ofthese elements. greater penetrating power than the cathode rays, areeffective to excite the particles below the The X-rays, having' surfaceof the screen, and, also, penetrate fur# sandth of one percent to onepercent, as'might be required.

The various Weights and temperatures given above are not critical in anystrict sense ofthe.

word, and may be varied over a wide range.

The 'amount of From the foregoing it will be seen that I have .t

provided an improved luminescent material which is an oxygen compound,and which comprises a metal and an element of the fourth vertical columnin the periodic system, and rhenium as an activator to give to thecompound the 'char-7 acteristic of becoming luminescent upon being.

excited. The term excited, as used alone herc-` y inbefore and in theclaims, is to be construed as meaning the condition assumed by thematerial when exposed to electron bombardment, X-rays', alpha-particles,or actinic light.

In making my improved material, as explained,

excellent luminescent materials are obtained since the resultantmaterial is for all intents and purposes homogeneous in its luminescentcharacteristics and properties. Ihis substantially homogeneity isobtained through the use of very finely divided dioxides of the elementsin group .IVof the periodic system. As pointed out above, by

using colloidal particles, their size is so small as' to possesspractically molecular dimensions, and accordingly, the resultantmaterial macroscopically is homogeneous.

It will be understood that modifications, within the conception of thoseskilled in the art, are possible without departing from the spirit of myinvention or the scope of the claims. l

I claim as my invention:

1. A metallic ortho-germanate activated by rhenium which gives to the'combination the characteristic of becoming luminescent upon be; ingexcited by radiant energy.

2. A metallic orthosilicate activated by rhenium which gives to thecombination the characteristic of becoming luminescent upon-'beingexcited by radiant energy.

3. A luminescent compound comprising a metal selected from thoseincluded in groups I through III of the periodic series 'of the elementscombined with an oxygen containing acid of a metal selected from groupIV of the periodic series of the elements, and a rhenium activator.

4. A luminescent composition of matter comprising a chemical compound ofzinc, an element selected from group IV of the periodic series of theelements and omgen, and a. rhenium acti vator.

5. The luminescent composition of -matter claimed in claim 4 comprisingin addition a minute amount of radio active material selected from thegroup consisting of radium, mesothorium, and actinium.

' 6. A luminescent compound comprising zinc orthosilicate and a rheniumactivator.

7. A luminescent compound comprising a. metallic orthosilicate and arhenium activator.

8. A luminescent compound comprising a metallic ortho-germanate and arhenium activator.

9. A macroscopically homogeneous luminescent compound, comprising a saltof a metal selected from group I through III of the periodic series withan oxygen containing acid of one of the elements of group IV of theperiodic series and rhenium as an activator.

HUMIBOLDT W. LEVERENZ.

